My laptop is pretty old and only has 240 mb of RAM. It is not extremely fast.
Although there may be other factors to my laptop's below average speed, I have been considering something: is Windows Defender slowing down my laptop?

With modern software, and only 240mbs of memory, anything running resident (which Defender is) will slow down your computer. If you really want Defender, perhaps you could look at the tools/options and stop anything you feel you can do without.

i will take that into consideration but i have another thought: if i have spy sweeper, will i need defender?

No. Most spyware programs are as good as, or superior to, Defender

thanks for the advice